Importance of modifiable non-radiographic functional parameters for adult spinal deformity

We clarified non-radiographic physical parameters associated with the severity of adult spinal deformity (ASD) using community-dwelling adult volunteers. They were subjected to upright entire spine radiographs for standard radiographic parameters and the number of sagittal modifiers of SRS-Schwab ASD classification (Schwab-SM). Clinical evaluations included isometric muscle strength of trunk extensor (TEX), trunk flexor (TFL), quadriceps femoris (QF), gluteus maximus, and iliopsoas; range of motion (ROM) of hip, knee, ankle, and active back extension (BET); SF36 physical component score (PCS), VAS for back and knee pain, and the degree of ambulatory kyphosis (dTIA). Each muscle strength was calibrated by body weight (BW) and expressed as BW ratio. According to our previous study, dTIA ≥ 7.6° was defined as pathological and dTIA ≤ 3.5° as normal. A final total of 409 female volunteers were included, and their demographics were; age 67.0 ± 5.5 years, Schwab-SM 2.1 ± 1.8, TEX 0.90 ± 0.33BW, TFL 0.48 ± 0.15BW, QF 0.45 ± 0.19BW, PCS 33.5 ± 6.5. Subjects were classified as clinical ASD group (cASD, n = 10) with PCS ≤ 27(mean-1SD) and pathological dTIA, robust group (n = 19) with PCS ≥ 40 (mean + 1SD) and normal dTIA, and the rest (non-cASD, n = 338). Statistical analyses showed significant differences in TEX, TFL, QF, knee extension (KEX), and BET between robust and cASD, and the mean values of robust group (TEX ≥ 1.1BW, TFL ≥ 0.5BW, QF ≥ 0.5BW, KEX ≥ 0° and BET ≥ 14 cm) were used as ‘ASD-MJ’ index. Subjects with fully achieving ASD-MJ goals showed significantly better radiographic and clinical outcomes than those with unmet goals. In conclusion, upon prescribing conservative or physical therapies for ASD patients, modifiable clinical goals should be clarified, and ASD-MJ could be a benchmark.

Clinical scores were conducted by spine physicians and physical therapists, and included visual analog scale for back and knee pain, and short form 36 (SF36) physical component scale summary (PCS).SF-36 is used to assess the health-related QoL (HRQoL), and a widely used generic instrument that measures eight types of health constructs.SF-36 PCS is composed of four primary items, including the summaries of physical functioning (10 items), role limitation due to physical problems (4 items), pain (2 items), and general health (5 items).The scores range from 0 to 100, with a higher score indicating better HRQoL.
Non-radiographic measurements by physical therapists included isometric muscle strength of trunk extensor (TEX), trunk flexor (TFL), quadriceps femoris (QF), gluteus maximus, and iliopsoas, using a chair-type GT350 of OG Giken Co., or a handheld dynamometer Mobie of Sakai Med Co., and each muscle strength was calibrated with body weight (BW) and expressed as BW ratio.Joint range of motion (ROM) was also measured; hip extension/internal rotation/external rotation, knee flexion/extension (KEX), ankle dorsiflexion.Radiographic measurements thoracic kyphosis (TK, between upper endplate of T4 and lower endplate of T12), lumbar lordosis (LL, between upper endplate of L1 and S1), sagittal vertical axis (SVA, distance of plumb lines through C7 and S1 posterior edge), sacral slope (SS, between upper sacral endplate and horizontal reference), pelvic tilt (PT, between the line through center of femoral head and midpoint of sacral table and vertical reference), pelvic incidence (PI, between the line through center of femoral head and midpoint of sacral table and the line perpendicular to sacral table), and percent slip (length of vertebral displacement divided by the length of vertebral endplate below; S/V in percent).TK thoracic kyphosis, LL lumbar lordosis, SVA sagittal vertical axis, SS sacral slope, PT pelvic tilt, PI pelvic incidence.
notch and floor at maximum active lumbar extension with thighs attached to the floor) and passive extension in prone-press test (distance of chin and floor at maximum lumbar extension at push-up with thighs attached to the floor).Each participant repeated the measurement at least three times, and best scores were used as flexor and extensor strength (Fig. 2).
Since vital characteristics of ASD has been specified as dynamic deformity 5,6 , which is the worsening of deformity during walk or prolonged daily activities, we evaluated ambulatory kyphosis with surface markers and video recorders.Each participant was instructed to walk 6-m walkway with surface markers attached on C7 (or on prominent cervical spinous process) and on L4 (or on intercrestal line).Trunk inclination angle (TIA, defined as angles subtended by the line through surface markers and the vertical reference) was measured at rest and during walk, and the difference in TIA (dTIA) was recorded as ambulatory kyphosis.Details of our measurements has been previously reported [7][8][9] .Each participant repeated dTIA measurement at least three times, and maximum difference was used.Most subjects showed increase in trunk inclination angle at walk, and dTIA was defined as positive for forward inclination (Fig. 3).
Statistical analysis was performed using the StatView software (Abacus Concepts, Inc, Berkley, CA).Interclass comparison was done by the analysis of variance, and p value of less than 0.05 was considered as a significant difference.Institutional review board approved the study, and written informed consent was mandatory for each participant upon enrollment.

Results
A final total of 409 female volunteers were included.Demographics and measured parameters are shown in Table 1.

Discussions
Recent multicenter studies indicated unsuccessful conservative treatment for ASD, and the mainstay of treating ASD has been surgery.
Acaroglu reported 1-year outcomes of 164 instrumented fusion cases and 371 conservative treatment cases of ASD, and indicated favorable outcomes were found in 42% of surgical cases and 6.7% of conservative cases.They showed that in most cases, the conservative treatment were mere observation and prescriptions, while 12 patients underwent physical therapy and 6 patients received invasive interventions such as injection therapy 3 .Glassman reported 5-year follow-up of 122 instrumented fusion cases and 73 conservative cases of ASD, and despite revision surgery in 24% and utilization of substantial resources in fusion cases, as-treated cost-effectiveness analysis favored surgery using the cumulative incremental cost-effectiveness ratio 1 .
Hoevenaars reported outcome of combined physical and psychological treatment for ASD patients (n = 80) and non-ASD patients (n = 240) with chronic low back pain.They showed that the ASD patients improved clinically as much as the non-ASD patients 10 .Hongo studied 102 Japanese women and reported that back extensor strength was significantly associated with LL and recommended back strengthening exercise for patients with kyphotic deformity 11 .Other studies also indicated the importance of back muscles, however, appropriate muscle load or targeted strength for each patient needed to be clarified.Proposed non-radiographic items, ASD-MJ, showed significant relation with radiographic and clinical outcomes, and subjects with back extensor strength of above 110% of BW, abdominal muscle strength of above 50% of BW, quadriceps strength of above 50% of BW, active back extension from prone position reaching 14 cm, and without knee flexion contractures were associated with less radiographic deformity and less back pain scores.
Limitation of our study included small number of subjects for heterogenic spinal deformity, yet this study included the largest-ever number with both radiographic and physical parameters including muscle strength and ROM.ASD-MJ was introduced using characteristic dynamic deformity and health-related quality of life (HRQoL) score, and showed significant relation with radiographic deformity and the number of Schwab-SM, however, this relation should be investigated further in interventional designs to confirm physical treatment effects for ASD.As an introductory for non-radiographic evaluation, this paper used the most popular Schwab-SM as radiographic parameters.Impact of coronal, axial, and other forms of ASD should be investigated in the future.Current ASD-MJ, using normative data from robust group, might be too strict to achieve, and data from non-cASD subjects, TEX ≥ 0.9BW, QF ≥ 0.5BW, KEX ≥ 0°, and BET ≥ 12 cm, provided comparable results and could be alternative goals for elderly patients with spinal deformity.www.nature.com/scientificreports/ In conclusion, modifiable clinical goals should be clarified upon prescribing conservative or physical therapies, and our results suggested improving trunk and thigh muscle strengths, and lumbar and knee ROMs could lead to improved HRQoL and radiographic ASD scores.Demonstrated ASD-MJ index could be a benchmark for successful comprehensive management of ever-increasing patients of ASD.
Figure1.Radiographic measurements thoracic kyphosis (TK, between upper endplate of T4 and lower endplate of T12), lumbar lordosis (LL, between upper endplate of L1 and S1), sagittal vertical axis (SVA, distance of plumb lines through C7 and S1 posterior edge), sacral slope (SS, between upper sacral endplate and horizontal reference), pelvic tilt (PT, between the line through center of femoral head and midpoint of sacral table and vertical reference), pelvic incidence (PI, between the line through center of femoral head and midpoint of sacral table and the line perpendicular to sacral table), and percent slip (length of vertebral displacement divided by the length of vertebral endplate below; S/V in percent).TK thoracic kyphosis, LL lumbar lordosis, SVA sagittal vertical axis, SS sacral slope, PT pelvic tilt, PI pelvic incidence.

Figure 2 .
Figure 2. Non-radiographic measurements Trunk flexor and extensor muscle strength measured using isometric device (GT350, OG Giken Co., Japan).Lower extremities muscle strength using isometric device (a handheld dynamometer Mobie of Sakai Med Co.).Active back extension test (BET: distance of sternal notch and floor at active lumbar extension).Passive prone-press test (distance of chin and floor at maximal lumbar extension by push-up force).ROM measurements of lower extremity.

Figure 3 .
Figure 3. Evaluation of Ambulatory Kyphosis.Trunk inclination angle was the angle subtended by the line through surface markers attached on C7 (or on prominent cervical spinous process) and on L4 (or on intercrestal line), and the line through vertical reference.Difference of trunk inclination angle (dTIA) between 6-m walk and rest was used and defined as positive for forward inclination during walk.Ambulatory kyphosis: angle a-b (dTIA).